sPatch is a very excellent 3-D modeller. It outputs to 3DS, RAW, and DXF formats. It’s a little scarce on the 'net these days, but if you do an internet search, one of the links will have it… It’s similar to Moray, but you can leave the model blank (Not textured) and then map it with a texture in OpenGL.

I tried the ones above, and it seems that moray will do the CSG, but that program isn’t exactly intuitive. The output format isn’t supported by anything I have yet, so that is another minus, not to mention that it wants povray for output. Other than that, it is OK.